Method and arrangement for controlling air resistance

ABSTRACT

A method for regulating during driving the air resistance to a leading and at least one following vehicle, whereby the distance of the leading vehicle from the following vehicle is detected and the magnitude of a wake formed behind the leading vehicle is regulated according to the detected distance in order to optimize the overall air resistance to the leading and the following vehicle. Also a device and a computer program and a computer program product for implementing the method.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method and a device for control of airresistance to vehicles. The invention also relates to a computer programfor implementing the method and a computer program product comprisingthe computer program.

BACKGROUND AND STATE OF THE ART

The air resistance to a vehicle leads to higher fuel consumption. Thereare therefore obvious advantages, both economic and environmental, inreducing the air resistance as much as possible.

One factor affecting the air resistance to a vehicle is the wake whichfollows a moving vehicle. The wake behind the vehicle is a region oflower than ambient air pressure, resulting in a braking effect on thevehicle. Various solutions have been put forward for reducing themagnitude of the wake and hence its influence on the air resistance tothe vehicle.

One solution is to use a so-called “boat tail”, i.e. a lengthening ofthe vehicle with a slope inwards relative to the vehicle's longitudinalaxis. The air is thus caused to flow better round the vehicle withoutseparation, thereby reducing the magnitude of the wake. However, thatsolution is not used very much, because it means sacrificing too muchcargo space, since vehicle maximum lengths are limited by laws andregulations.

Another solution which has the same effect as the above solution is tomake the rear of the vehicle rounded and use so-called active boundarylayer control. This entails air being sucked or blown through a narrowgap at the rear of the vehicle so as to cause air streaming past thevehicle to flow round the vehicle without separation. This is a knowntechnique from aircraft.

In convoy driving, however, the wake behind a vehicle may be anadvantage in that the vehicle behind derives benefit from the lower airpressure in the wake of the vehicle ahead and is thereby subject tolower air resistance. The various solutions for reducing the magnitudeof the wake may thus entail a disadvantage in convoy driving, bydepriving the following vehicles in the convoy of the air resistancereducing effect of the wake.

SUMMARY OF THE INVENTION

One object of the present invention is to provide regulating of airresistance to vehicles whereby the air resistance is optimised both insingle driving, i.e. with a single vehicle, and in convoy driving, i.e.with two or more vehicles following one another.

This is achieved by a method for regulating during driving the airresistance to a leading vehicle and at least one vehicle following itwhereby the distance between the leading and following vehicles isdetected and the magnitude of a wake formed behind the leading vehicleis regulated on the basis of the detected distance in order to optimisethe overall air resistance to the leading and following vehicles. Theresult is a method which optimises the air resistance in various drivingsituations.

With advantage, the regulating of the magnitude of the wake behind theleading vehicle is switched off when the distance between the latter andthe following vehicle decreases to below a predetermined value. Thisprovides a simple and reliable indication of how best to regulate theair resistance.

The object is also achieved by a device for regulating during drivingthe air resistance to a leading vehicle and a following vehicle, whichdevice comprises means for regulating the magnitude of a wake formedbehind the leading vehicle and also comprises a distance sensor formeasuring the distance between the leading and the following vehicle,and a control device for controlling the means for regulating themagnitude of the wake on the basis of the distance detected by thesensor, in order to optimise the overall air resistance to the leadingand the following vehicle. This device can be used to optimise the airresistance in various driving situations.

The invention also relates to a computer program comprisingcomputer-readable code means which, when run on a computer, causes acontrol device to implement the above method, and a computer programproduct comprising a support and said computer program, the computerprogram being recorded on the support. The result is a simple way totake care of regulating the air resistance without burdening the driverwith extra tasks.

DESCRIPTION OF THE DRAWINGS

The invention is described below with reference to the attacheddrawings, in which:

FIG. 1 depicts schematically a vehicle without active boundary layercontrol;

FIG. 2 depicts schematically a vehicle with active boundary layercontrol;

FIG. 3 depicts schematically a control device in cutaway section; and

FIGS. 4 a-c depict flowcharts of various embodiments of the methodaccording to the invention.

DESCRIPTION OF EMBODIMENTS

When a vehicle 1 is in motion, the air flow about the vehicle results inthe formation of a wake 2 behind the vehicle 1. In the wake 2, a lowerthan ambient air pressure prevails, causing a braking effect on thevehicle 1. FIG. 1 and FIG. 2 depict schematically two different airflows about a vehicle 1. The lines outside the vehicle 1 at the rearedge 3 of the vehicle 1, and the lines behind the vehicle 1, representthe air flow at the rear edge 3 and in the wake 2.

Ways of reducing the magnitude of the wake 2, as illustrated in FIG. 2,include having the rear edge 3 of the vehicle 1 rounded and usingso-called active boundary layer control. These measures reduce themagnitude of the wake, making it possible to lower the air resistance byabout 10-20% and hence reduce fuel consumption. Active boundary layercontrol involves using, for example, a pump or a compressor 4 forsucking or blowing air (represented schematically in FIG. 2 bychain-dotted arrows) through a narrow gap 5 around the vehicle 1, justahead of the radius at the vehicle's rear edge 3. The air streaming pastthe vehicle 1 is thus made to flow round the vehicle without separation,thereby reducing the magnitude of the wake 2.

Convoy driving of vehicles 1, e.g. trucks and buses, reduces the airresistance to the following vehicles in the convoy through their beingable to derive benefit from the wake 2, with its lower air pressure,behind the vehicle ahead. A convoy with a distance between vehicles ofabout 40 metres, at a speed of about 80 km/h, may reduce the airresistance to the second vehicle by about 20% and that to the third andfther vehicles by about 30%.

However, a vehicle using active boundary layer control destroys thepossibility of utilising its wake to reduce air resistance to followingvehicles in a convoy. The active boundary layer control of the vehicle 1in FIG. 2 is therefore arranged so that it can when necessary beswitched off to enable following vehicles in the convoy to derivebenefit from the wake.

Switching the active boundary layer control off may be effected invarious ways. For example, the driver of the vehicle 1 may switch thecompressor 4 off manually when there are vehicles in convoy behind theleading vehicle 1. The driver may with advantage be assisted in this bythere being on the rear wall of the vehicle 1 a conventional distancesensor 6 which measures the distance from the vehicle behind. Thisenables the driver to switch the active boundary layer control off attimes when the air resistance to vehicles behind the driver's vehicle 1may be assumed to decrease more than the air resistance to the driver'svehicle 1 increases. The result is optimisation of the overall airresistance to the vehicles concerned. A distance from the vehicle behindwhich may be suitable for switching the active boundary layer controloff is about 100 metres, but this distance may vary in differentoperating situations with different sizes of vehicles, different speedsetc.

The vehicle 1 in FIG. 2 incorporates a control device 7 which isdepicted in more detail in FIG. 3. The control device comprises a knowntype of computer 8, e.g. a microprocessor. The computer 8 receives via aport P₁ of the control device 7 signals corresponding to informationfrom the distance sensor 6, and possibly via other undepicted portssignals corresponding to information from other sensors normally presentin a vehicle, e.g. speedometer etc. The computer 8 then uses informationabout, for example, the vehicle's speed and the distance from thevehicle behind to calculate whether it is advantageous to switch theactive boundary layer control off. If such is the case, signalscorresponding to information about switching are sent via a port P₂ tothe compressor 4, whereupon the compressor 4 shuts down. The computer 8may of course also be arranged to inform the driver when it isadvantageous to switch off the active boundary layer control off,whereupon the driver can effect switching off manually. The computer 8works on the basis of what is indicated in the computer program which isstored on some form of support 9, e.g. a flash memory, ROM memory, EPROMor some other non-volatile memory, which support is read by the computer8. The control device may comprise a port P₃ via which the support 9 canbe loaded with the computer program. The computer program may thus bestored on a support in the form of a CD-ROM or the like and bedownloaded to the support 9 via port P₃. Communication between thecomputer 8 and respectively the support 9 and ports P₁-P₃, and betweenthe computer 8 and the support 9, takes place advantageously viadatabuses B₁-B₄, and communication between the control device andrespectively the distance sensor 6 and the compressor 4, whichcommunication in FIG. 2 is schematically represented by broken lines,takes place, for example, via CAN buses.

If the distance from the vehicle behind subsequently increases so muchthat, with the active boundary layer control switched off, the airresistance to the vehicle behind the driver's vehicle 1 no longerdecreases more than the air resistance to the driver's vehicle 1increases, the computer 8 sends signals corresponding to informationabout switching on the compressor 4. The active boundary layer controlis thus switched on again automatically when this is advantageous.Switching on may of course also be effected manually by the driver onthe basis of his/her own assessment of when it is time to do so, or onthe basis of information from the computer 8 concerning when it is timeto effect switching on.

The control signal to the means 4, 5 for regulating the magnitude of thewake 2 is described above as a signal corresponding to regulating in theform of switching the active boundary layer control on or off, but asignal corresponding to regulating in the form of decreasing orincreasing the active boundary layer control is also conceivable. Suchdecrease and increase may with advantage be effected by altering the airflow through the compressor 4 and the gap 5.

FIGS. 4 a- 4c depict schematically various embodiments of the methodaccording to the invention in the form of flowcharts. In the methodaccording to FIG. 4 a, everything is taken care of automatically. Thedistance from the vehicle behind is detected (step SI) and informationconcerning that distance is sent to the computer 8 which, on the basisof what is indicated in a computer program stored on the support 9,processes-this and any other information received (S₂), followed by theresult of this information processing being sent in the form of acontrol signal to the means 4, 5 for regulating the magnitude of thewake 2 formed behind the leading vehicle 1 (step S₃).

In the method according to FIG. 4 b, steps S₁ and S₂ are the same as inthe method according to FIG. 4 a, but the information is sent instead tothe driver, who may decide whether the regulating of the magnitude ofthe wake should be altered (step S₄), followed by the magnitude of thewake being regulated in response to command from the driver (step S₅).The driver may with advantage receive information from step S₂ presentedon a display on the dashboard or the like, and communication to and fromthe driver is advantageously via CAN buses.

The method according to FIG. 4 c differs from the method according toFIG. 4 b in that the driver also takes care of detecting the distance(step S₆). This detection is effected with advantage by visual judging,e.g. via rear view mirrors, of the distance from the vehicle behind.

The invention described above makes it possible to minimise airresistance in both single driving and convoy driving. Lower airresistance also means lower fuel consumption. It may be mentioned forexample, that convoy driving with distances of between 20 and 80 metresbetween vehicles results in average fuel savings of almost 9%. Thecloser together the vehicles, the greater the fuel saving. It should benoted, however, that a distance of about 40 metres between vehicles hasnormally to be maintained as safety distance in convoy driving at about80 km/h to enable drivers to react in good time when decelerationoccurs.

It is with advantage also possible for the driver to be able to regulatethe active boundary layer control manually even if the latter isarranged, as in FIG. 4 a, to be regulated entirely automatically, e.g.for him/her to be able to opt to keep the active boundary layer controlswitched on at times when optimisation of the overall air resistance tothe leading and the following vehicle would entail it being switchedoff, if for any reason the driver considers it more important to reducethe air resistance to the leading vehicle than to that/those behind.

1. A method for regulating during driving the air resistance to aleading and at least one following vehicle, the method comprisingdetecting the distance of the leading vehicle from the at least onefollowing vehicle is and regulating the magnitude of a wake formedbehind the leading vehicle according to the detected distance betweenthe leading and the following vehicles in order to optimize the overallair resistance to both the leading and the at least one followingvehicle.
 2. A method according to claim 1, wherein the regulating of themagnitude of the wake behind the leading vehicle comprises reducing orswitching off the regulating of the wake when the distance between theleading and the at least one following vehicle decreases to below apredetermined value.
 3. A device for regulating during driving the airresistance to a leading and at least one following vehicle, comprisingapparatus at the leading vehicle operable for regulating the magnitudeof a wake formed behind the leading vehicle comprising a distance sensorat the leading vehicle operable for measuring the distance between theleading and the at least one following vehicle, and a control deviceoperable for controlling the apparatus for regulating the magnitude ofthe wake according to the distance detected by the sensor, in order tooptimize the overall air resistance to the leading and the followingvehicle.
 4. A computer program comprising computer-readable code which,when run on a computer, causes a control device to regulate duringdriving the air resistance to a leading and at least one followingvehicle by detecting the distance of the leading vehicle from the atleast one following vehicle and regulating the magnitude of a wakeformed behind the leading vehicle according to the detected distancebetween the leading and the following vehicles in order to optimize theoverall air resistance to both the leading and the at least onefollowing vehicle.
 5. A computer program product comprising a supportand a computer program according to claim 4, and the computer program isrecorded on the support.
 6. A method according to claim 2, wherein theregulating further comprises switching on or increasing the magnitude ofthe wake as the distance between the leading and the at least onefollowing vehicle increases above a respective predetermined value.
 7. Amethod according to claim 6, wherein the regulating further comprisesswitching off or decreasing the magnitude as the distance between theleading and the at least one following vehicle deceases below inrespective predetermined value.
 8. A device according to claim 3,wherein the apparatus operable comprises an air flow device operativefor affecting air flow past the vehicle for regulating the wake.
 9. Adevice according to claim 7, wherein the air flow device is operable todirect air inwardly from a surface of the vehicle past which air flowsduring driving.